The present invention relates, in a high-efficiency coding for converting a picture into a digital signal with less code amount in order to transmit, store and display the picture efficiently, to the procedure particularly for coding a picture in block unit.
In the coding of pictures, the procedure for coding pictures in block unit using Discrete Cosine Transform (DCT) or the like has been most generally used.
There is a method for predicting pixels of a block to be coded from a coded block and for coding a predicted residue thereof, instead of coding blocks independently.
For example, refer to "High-Efficiency Coding of Pictures by Extrapolative Prediction--Discrete Sine Transform" described in the literature in Society of Electronic Information Communications (B), J71-No.6,pp. 717-724 (June 1988) and the like.
According to the literature, the coding processing is sequentially carried out in block unit, so that a coded block is present only on one side of a block to be coded. Accordingly, inter-block prediction is performed in one direction where a coded block is present. This prediction is called extrapolative prediction.
In the coding of a residual signal of the inter-block prediction, it is known that Discrete Sine Transform (DST) is higher than DCT in coding efficiency. This method employs inter-block correlation, so that the coding efficiency is better than intra-block coding. Further, in the inter-block prediction, predictive signals are obtained in a continuous signal value from an adjacent block to a block to be coded. Thus, even if the prediction residue is not completely coded, the continuity over blocks is improved and a block distortion is hard to occur.
However, as described above, the conventional inter-block prediction is performed using only one coded block presented one direction with respect to a block to be coded. In this case, the change of picture cannot be well predicted, and the coding efficiency is not sufficiently improved.
Further, the inter-block prediction is a cyclic prediction. Therefore, pictures will be damaged when a coding error occurs in a transmission line connecting an inter-block coding apparatus and a storage medium, an inter-block decoding apparatus, etc.